Docs update

editions/tw5.com/tiddlers/concepts/CurrentTiddler.tid

@@ -5,3 +5,5 @@ title: CurrentTiddler
 type: text/vnd.tiddlywiki
 
 The CurrentTiddler is the current tiddler during WikiText processing. A context tiddler is set by the TiddlerWidget. It allows you to write references like `<$view field="title" format="link"/>` in TemplateTiddlers without explicitly specifying the tiddler that it applies to.
+
+The title of the current tiddler is contained in the widget variable ''currentTiddler''.

editions/tw5.com/tiddlers/widgets/TiddlerWidget.tid

@@ -1,5 +1,5 @@
 created: 20130824154300000
-modified: 20140107114152456
+modified: 20140802114152456
 tags: widget
 title: TiddlerWidget
 type: text/vnd.tiddlywiki
@@ -13,3 +13,23 @@ The TiddlerWidget sets the CurrentTiddler that applies for processing its conten
 |!Attribute |!Description |
 |tiddler |The title of the tiddler to become the new CurrentTiddler |
 |class |CSS classes to added to the generated elements |
+
+! CSS Class Variables
+
+The tiddler widget assigns several useful CSS classes to variables that it creates:
+
+* ''missingTiddlerClass'': ''"tw-tiddler-exists"'' or ''"tw-tiddler-missing"'' depending upon whether the target tiddler exists
+* ''shadowTiddlerClass'': ''"tw-tiddler-shadow"'' if the tiddler is a shadow tiddler
+* ''systemTiddlerClass'': ''"tw-tiddler-system"'' if the tiddler is a system tiddler
+* ''tiddlerTagClasses'': A space separated list of CSS classes named ''"tw-tagged-{tagname}"''. For example ''"tw-tagged-introduction"''. Note that tag names are UrlEncoded which means that the tag ''$:/tags/Macro'' appears as the CSS class ''"tw-tagged-%24%3A%2Ftags%2FMacro"''
+
+You can use these variables like this:
+
+```
+<$tiddler tiddler="MyOtherTiddler">
+<div class=<<missingTiddlerClass>>>
+<$transclude/>
+</$tiddler>
+```
+
+See also [[$:/core/ui/ViewTemplate]].